I have about 20 years experience as a lawyer, and dabbled in criminal law only for the first few years, and then did not touch it at all for many years, and am now doing a very large percentage of work in the area.
I can tell you that the learning curve to jump into the area is a bit steep, but it sounds as though you have more experience than I did when I resumed my criminal practice. I did not find the readjustment to be that daunting. But I also am in a situation where I can bounce ideas off a large number of colleagues who also do criminal law, which has helped a great deal.
The law has not changed so drastically in the last 10 years or so that you would not be able to readjust. There have been a few decisions that impact on many Charter arguments (R. v. Grant from the SCC is a key one for all defence counsel), but no wholescale changes to the law.
So learning the law would not be the major challenge to you, in my view. It would be getting paying clients in the door.
Most criminal law lawyers I know are now doing quite well, better than they were when I first started. At that time, it was a difficult area to break into, as the economy was terrible, and it seemed that no one had money to pay a lawyer except for major, serious files, which would not go to junior or inexperienced lawyers. Now, it seems that there is a large number of people that are willing and able to pay sizable retainers to defend matters, as the economy is much better. Also, the bread and butter files of impaired driving are much more common due to crackdowns by police, and people wish to dispute them more as they can now prevent travel to the U.S. on conviction, and the mandatory minimums on repeat offences have increased. Plus, serious drug offences are more likely to be defended than a simple guilty plea given the mandatory minimums that are involved. So generally, it is a fairly lucrative time to start such a practice. We see people that seem to have a fairly healthy practice after a year or two.
As for age, that could work to your benefit as clients will assume you have many years of experience. I don't think being 55 is any bar to starting up a practice, and it may actually make it easier than starting out at 25 due to the respect that age inevitably brings with it.
If you can find a situation where you can work as an employee and perhaps slowly grow some client base/experience/reputation, that is ideal. As for whether you could survive some time with a low client base - it depends on your resources and what those few clients pay. Certainly many of the costs associated with being in private practice such as rent, staffing costs, access to a legal database, and so on have all increased dramatically in the last 10 years as well. So certainly the first year or two could be quite lean on the botXXXXX XXXXXne and would not be without risk.
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